Systemic Lupus Erythematosus (SLE) is the prototype autoimmune disease, characterized clinically by glomerulonephritis and vasculitis and immunologically by the production of multiple autoantibodies. Of these autoantibodies, antibodies (Abs) to dsDNA correlate strongly with disease activity, and evidence suggests they play a direct role in the pathogenesis of tissue damage. DNA Abs could potentially exert their pathogenic effects in 3 ways: 1.) binding to DNA to form pathogenic immune complexes (IC), 2.) binding directly to tissue antigens, or 3.) directly modifying cell function. The focus of this grant has been to study the formation and clearance of DNA IC; we have studied the clearance of extracellular DNA to investigate how DNA might become available for Ab binding, and we have studied the in vivo behavior of model DNA IC. During these studies, we identified a subset of DNA Abs, the presence of which correlates with SLE disease activity. We now propose: 1.) to characterize this subset of DNA Abs to understand its pathogenicity, 2.) to extend our studies on DNA IC, and 3.) to begin studies on mechanisms by which DNA Abs might be pathogenic other than by the formation of DNA IC. 1.) Ab subsets which bind DNA by monogamous bivalent binding or by cross-linking DNA have been identified. The basis for this difference will be studied by examining the binding specificity and avidity of each Ab type. Clinical associations with each Ab type will be sought. 2) The in vivo behavior of defined IC made with both Ab subsets will be examined (mice); the effect of IC size and Ab/Ag ratio will be studied. Since DNA binds to Clq, we will also study C1 activation of these DNA IC. To examine the possibility that DNA Abs cross-react with tissue antigens, binding of DNA Abs directly to renal tissue will be studied using a renal perfusion model. 3.) The DNA receptor will be isolated from Kupffer cells and characterized. These studies should define parameters which control the clearance of DNA IC, and directly address the question of cross- reactivity of DNA Abs with tissue (renal) antigens. In addition, we will begin to address the broader question of the physiologic role of the DNA receptor.